This invention relates to high-definition television (HDTV) systems.
Due largely to the development of the Japanese HDTV system, there is a great deal of interest in the design of systems that would feature better performance than the NTSC system now used in the U.S. Various systems have been proposed having improved spatial resolution, a wider aspect ratio, and free of NTSC defects due to interlace and to crosstalk between luminance and chrominance.
A very important feature of new systems is whether they are "receiver-compatible," which means that existing receivers would be able to decode and display the new transmissions. Another important feature is "channel compatibility," which means that the new signals could be transmitted properly in the 6-MHz channels now used for NTSC. Present broadcasters believe that receiver compatibility is necessary in order to continue serving the existing 140 million NTSC receivers. Unfortunately, the incorporation of the NTSC signal structure in new systems means that they will be inefficient in the transmission of information, and that it will therefore be impossible to achieve true HDTV performance with such receiver-compatible systems. One proposal is to start with an intermediate quality enhanced-definition (EDTV) system that is receiver-compatible and then move to a noncompatible system in a later stage. To employ this strategy the EDTV system must be a technological "bridge" to the final system, and preferably should be compatible with the new receivers to be used in the final system.
In the case of cable transmission, receiver compatibility is not required, since access is controlled anyway. The viewer must pay to see programs, and must have a new receiver to see them.